Caption: Viruses and protozoa, abstract illustration. The protozoa shown here are Paramecium (elongated shapes), a type of unicellular ciliated protozoa found in a wide range of freshwater and marine environments. The viruses are the circular and icosahedral shapes. Examples of viruses associated with Paramecium protozoa are the Chlorovirus viruses, such as Paramecium bursaria Chlorella virus 1 (PBCV-1).